Freezer Alarm (024)

I am studying an electronics course at School of Electronics and Aaeronautical Engineering (SEAE), military school. As a projects i am to design and make a freezer alarm. This alarm has to sound a siren and flash lights when the door is left open for more than 20 seconds and the temperature drops out of the range -20 degrees to +30 degrees. If you have any suggestions or ideas of this project i would be greatful

If the door is left open, you won't have to worry about the -20 degree end of the range.
Have a look at LM34 or LM35, and a comparator such as LM393. Use a dual timer (LM556) for the flashing lights and siren. You might also need a precision reference such as LM399.

I have exactally what you need. Well, minus the temperature part. https://www.redcircuits.com/Page15.htm Hope it helps.

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